U.S. patent application number 10/886377 was filed with the patent office on 2006-01-12 for display member incorporating a patterned adhesive layer.
Invention is credited to Man C. Tam.
Application Number | 20060007524 10/886377 |
Document ID | / |
Family ID | 35541053 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060007524 |
Kind Code |
A1 |
Tam; Man C. |
January 12, 2006 |
Display member incorporating a patterned adhesive layer
Abstract
A display medium including bichromal or multichromal display
elements incorporates a patterned adhesive layer to position the
display elements in a closely-packed monolayer. The closely-packed
monolayer may provide improved contrast, brightness and image
quality. A method of making such a display medium includes forming
a patterned adhesive layer over a substrate and cascading display
elements over the patterned adhesive layer, optionally several
times to form a substantially uniform monolayer.
Inventors: |
Tam; Man C.; (Mississauge,
CA) |
Correspondence
Address: |
PEPPER HAMILTON LLP
ONE MELLON CENTER, 50TH FLOOR
500 GRANT STREET
PITTSBURGH
PA
15219
US
|
Family ID: |
35541053 |
Appl. No.: |
10/886377 |
Filed: |
July 7, 2004 |
Current U.S.
Class: |
359/296 |
Current CPC
Class: |
G02B 26/026
20130101 |
Class at
Publication: |
359/296 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. An image formation member, comprising: a conductive substrate; a
patterned adhesive layer on the substrate; a plurality of capsules
on the patterned adhesive layer, wherein the capsules are
positioned in a monolayer in a pattern that substantially
corresponds to the pattern of the patterned adhesive layer; and a
conductive layer positioned over the capsules and opposite from the
patterned adhesive layer, wherein the conductive layer is at least
substantially transparent.
2. The member of claim 1 wherein the patterned adhesive layer
comprises a pattern of raised adhesive elements that project from
the conductive substrate.
3. The member of claim 2, wherein: the capsules have a
substantially uniform diameter; and the raised adhesive elements
are spaced apart such that center-to-center spacing of the raised
adhesive elements is slightly more than the diameter of the
capsules.
4. The member of claim 2 wherein: the capsules have a substantially
uniform diameter; and the raised adhesive elements have a width
that is between about 5% and about 50% of the diameter of the
capsules.
5. The member of claim 2 wherein the pattern comprises an at least
substantially hexagonal array.
6. The member of claim 1 wherein the patterned adhesive layer
comprises at least one of a pressure-sensitive adhesive, a
heat-activated adhesive, and a light-activated adhesive.
7. The member of claim 1 wherein the patterned adhesive layer
comprises at least one of a copolymer of styrene and acrylate, a
polyester resin, polyurethane, a copolymer of acrylonitrile and
vinylidene chloride, polyvinyl acetate, polyvinyl butyral,
polyolefin and an epoxy.
8. The member of claim 1 wherein the capsules are dispersed in a
transparent matrix medium that is positioned between the conductive
substrate and the transparent conductive layer.
9. A display medium, comprising: a substrate; a patterned adhesive
layer on the substrate; a plurality of display elements on the
patterned adhesive layer, wherein: the patterned adhesive layer
comprises a pattern of raised adhesive elements that project from
the substrate; the display elements are positioned in a monolayer
in a pattern that substantially corresponds to the pattern of the
patterned adhesive layer; the display elements have a substantially
uniform width; and the raised adhesive elements are spaced apart
such that center-to-center spacing of the raised adhesive elements
is slightly more than the width of the display elements; and an
overlayer positioned over the display elements and opposite from
the patterned adhesive layer, wherein the overlayer is at least
substantially transparent.
10. The display medium of claim 9, wherein the raised adhesive
elements have a width that is between and 5% and about 50% of the
width of the display elements.
11. The display medium of claim 9 wherein the display elements
comprise one or more of bichromal or multichromal particles, beads,
capsules, cylinders or balls.
12. The display medium of claim 9 wherein the patterned adhesive
layer comprises at least one of a copolymer of styrene and
acrylate, a polyester resin, polyurethane, a copolymer of
acrylonitrile and vinylidene chloride, polyvinyl acetate, polyvinyl
butyral, polyolefin and an epoxy.
13. A method of manufacturing a display medium, comprising:
applying an adhesive material to a substrate, wherein the adhesive
material is passed through a patterned screen before reaching the
substrate so that the adhesive material forms a patterned adhesive
layer on the substrate, wherein the pattern of the patterned
adhesive layer corresponds to the pattern of the patterned screen;
depositing a plurality of bichromal capsules on the patterned
adhesive layer so that the capsules form a monolayer in positions
that at least substantially correspond to the pattern of the
patterned screen; and placing a conductive layer on the monolayer
of capsules.
14. The method of claim 13 wherein the depositing step is repeated
a plurality of times to provide a substantially uniform
monolayer.
15. The method of claim 13 further comprising, after the depositing
step, removing capsules that do not adhere to the patterned
adhesive layer.
16. The method of claim 13 wherein the applying step comprises one
or more of screen printing, ink jet printing, spray coating and
gravure roll coating.
17. The method of claim 13 wherein the patterned adhesive layer
comprises a light-activated adhesive, and the applying step
comprises photo patterning.
18. The method of claim 13 further comprising vibrating the
substrate during or after the depositing step.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The description set forth herein generally relates to
display members and methods of manufacturing them. More
particularly, the description relates to electronic paper-type
displays and display members that include a patterned adhesive
layer.
[0003] 2. Description of Related Art
[0004] Display technologies based on encapsulation of
electrophoretic particles, multichromal beads and liquid crystals
have many potential applications in fields such as electronic paper
and other digital document media. Examples of such electronic
display devices include those available from Gyricon LLC of Ann
Arbor, Mich. For example, as shown in FIG. 1, a group of bichromal
beads, cylinders, crystals or other bichromal or multichromal
particles 10 are dispersed in an elastomeric sheet swollen by a
fluid 12 and positioned atop a conductive substrate 14 such as a
printed circuit board. The particles, fluid and substrate are
covered with a transparent layer 16 such as glass or plastic and a
transparent conductive material such as indium tin oxide (ITO) 18,
and they are sealed to form a re-addressable display material in
which the particles rotate in response to an electric or magnetic
field that is applied to the conductive substrate.
[0005] Bichromal displays have numerous advantages over
conventional electrically addressable visual displays, such as LCD
and CRT displays. In particular, they are suitable for viewing in
ambient light, they retain an image indefinitely in the absence of
an applied electric field, and they can be made lightweight,
flexible, foldable, and with many other familiar and useful
characteristics of ordinary writing paper. Thus, at least in
principle, they are suitable both for display applications and for
so-called electric paper or interactive paper applications, in
which they serve as an electrically addressable, reusable
substitute for ordinary paper. For further advantages of the
bichromal display, see, for example, U.S. Pat. No. 5,389,945, which
is herein incorporated by reference.
[0006] Current multichromal display devices are often produced by
the "swollen sheet" method. In this method, bare multichromal
beads, randomly mixed and dispersed in a silicone elastomeric
sheet, are rendered rotatable by swelling the elastomer in silicone
oil. Pockets of oil form around each bead, and the beads detach
from the elastomer-bead interface. The resulting device thus
includes a swollen elastomeric coating of bichromal particles.
Additional detail about the swollen sheet production method may be
found in, for example, U.S. Pat. No. 6,441,946, which is
incorporated herein by reference in its entirety.
[0007] The current swollen sheet methods may result in a display
layer that exhibits an undesirably low white reflectance in the
background area of the displayed image. Consequently, the
background area may appear objectionably dark gray rather than
white to the viewer. High white reflectance is desirable in order
to provide a higher contrast between the displayed image and the
background. Examples of low white reflectance in current devices
include levels under about 17%. These levels may result from the
upper-level bichromal beads (i.e., those closest to the transparent
layer and furthest from the conductive substrate) being spaced
further apart than the lower-level beads. In some cases, the
upper-level beads can cover less than 20% of the surface area. Low
white reflectance may result when light passes through the
interstices in the upper-level beads, is scattered and absorbed by
the darker hemispheres of the beads, and is not reflected back to
the observer.
[0008] In addition, the swollen sheet method can result in a
display layer that requires a relatively high switching voltage in
order to rotate the beads in the layer, since the layer is thickly
coated and sealed in order to contain the swelling fluid.
Furthermore, the elastomer sheet must be kept wet with oil in order
for the capsules to maintain their rotation capabilities, as oil
evaporation can cause collapse of the display layer cavity and
result in immobilization of the beads. Plus, the display device
must be sealed to contain the swelling fluid, resulting in
increased cost and complexity.
[0009] To solve at least some of the problems listed above, U.S.
Pat. No. 6,445,496, which is incorporated herein by reference in
its entirety, describes a method of encapsulating the bichromal
balls within an oil-filled capsule. The capsule is formed by
chemical means. Encapsulation may eliminate the need for a costly
elastomer and the sealing step. U.S. Pat. No. 6,492,025,
incorporated herein by reference, describes an example of
microcapsule composition. U.S. Pat. No. 6,488,870, incorporated
herein by reference, describes examples of additional encapsulation
processes. A display device describing a closely-packed monolayer
of encapsulated bichromal balls is described in co-pending U.S.
patent application No. _____, entitled "Contrast Enhancement in
Multichromal Display by Incorporating a Highly Absorptive Layer,"
filed Jul. 7, 2004, which is incorporated herein by reference in
its entirety. Such a device may exhibit an improved white
reflectance (e.g., in the range of about 20% to about 30%). In
addition, it allows a thinner coating, thus enabling a lower
switching voltage to be used to drive rotation of the beads.
[0010] During fabrication of a device using a closely-packed
monolayer of encapsulated bichromal balls, the position of the
capsules may become fixed once they come into contact with the
adhesive layer. For example, as shown in FIG. 2, if the capsules 10
are spaced so that they are close enough to prohibit other beads
from resting between the space (i.e., not near touching but less
than one capsule diameter apart), the interstitial space 20 between
the capsules will not accommodate another capsule. Accordingly,
either a monolayer will not result, or the upper layers will
cascade off of the monolayer. In either situation, packing will be
less dense, and contrast and brightness will be diminished.
[0011] Accordingly, a need exists for a display device that is
manufactured using an improved method of forming a monolayer of
encapsulated beads.
SUMMARY
[0012] In an embodiment, a display medium includes a substrate, a
patterned adhesive layer on the substrate, and a number of display
elements on the patterned adhesive layer. An at least substantially
transparent overlayer, such as a counterelectrode, may be
positioned over the display elements and opposite from the
patterned adhesive layer. In an embodiment, the patterned adhesive
layer forms a pattern of raised adhesive elements that project from
the substrate. The display elements may be positioned in a
monolayer in a pattern that substantially corresponds to the
pattern of the patterned adhesive layer. In an embodiment, the
display elements may have a substantially uniform diameter, and the
raised adhesive elements may be spaced apart such that
center-to-center spacing of the raised adhesive elements is
slightly more than the diameter of the display elements.
[0013] Optionally, the raised adhesive elements have a lateral area
(or width) that is between and about 5% and about 50% of the
diameter of the display elements, although other sizes are
possible. The display elements may include, and are not limited to,
one or more of bichromal or multichromal particles, beads,
capsules, cylinders or balls. The patterned adhesive layer may be
made of a copolymer of styrene and acrylate, a polyester resin,
polyurethane, a copolymer of acrylonitrile and vinylidene chloride,
polyvinyl acetate, polyvinyl butyral, polyolefin, an epoxy, and/or
another material.
[0014] In another embodiment, a method of manufacturing a display
medium includes applying an adhesive material to a substrate. The
adhesive material is passed through a patterned screen before
reaching the substrate so that the adhesive material forms a
patterned adhesive layer on the substrate. Suitable application
methods include, and are not limited to, screen printing, ink jet
printing, spray coating, gravure roll coating and/or other methods.
When the patterned adhesive layer is made of a light-activated
adhesive, the depositing step may also include photo patterning.
The pattern of the patterned adhesive layer corresponds to the
pattern of the patterned screen. The method also includes
depositing a plurality of bichromal capsules on the patterned
adhesive layer so that the capsules form a monolayer in positions
that at least substantially correspond to the pattern of the
patterned screen. The method also includes placing a conductive
layer on the monolayer of capsules.
[0015] Optionally, the step of depositing capsules may be repeated
two or more times to provide a substantially uniform monolayer.
Also optionally, after the depositing step, capsules that do not
adhere to the patterned adhesive layer may be removed. Optionally,
the method may include vibrating the substrate during or after the
depositing step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a side view of exemplary elements of a
prior art electronic display.
[0017] FIG. 2 illustrates a side view of exemplary elements of a
display member with a monolayer of beads but having undesired
spacing between the bichromal capsules.
[0018] FIG. 3 illustrates a side view of a display member with a
monolayer of capsules having improved spacing between the bichromal
capsules.
[0019] FIG. 4 illustrates a side view of a substrate for a display
member with a patterned adhesive layer positioned atop the
substrate.
[0020] FIG. 5 illustrates a top view of an exemplary adhesive layer
pattern.
[0021] FIG. 6 illustrates the view of FIG. 5 with a layer of
capsules atop the adhesive layer.
[0022] FIG. 7 illustrates a side view of a display member with an
optional transparent layer.
DETAILED DESCRIPTION
Notations and Nomenclature
[0023] As used herein, the words "bichromal" and "multichromal"
will be used interchangeably to refer to a display or a particle
that may exhibit two or more colors. In addition, the words "bead",
"particle" and "capsule" are used interchangeably to refer to a
bichromal element for a display medium, such as a twisting
cylinder, microcapsule, bead, electrophoretic material or any other
bichromal or multichromal material that may be modulated by an
applied electric or magnetic field. For example, a bichromal bead
in an oil-filled capsule may rotate inside the capsule in response
to the applied field.
DESCRIPTION
[0024] The description that follows generally relates to display
members and methods of manufacturing them. In an embodiment, the
description relates to electronic paper-type displays and display
members that include a patterned adhesive layer
[0025] FIG. 3 illustrates exemplary elements of a display member
according to one embodiment. The display member includes an image
formation layer that includes a single layer, or monolayer, of
encapsulated particles 10 positioned atop a conductive substrate
14. The conductive substrate 14 may be paper, conductive plastic, a
printed circuit board or other material that may apply or pass a
field to selected particles in the image formation layer. Between
the particles 10 and the substrate 14 is a patterned adhesive layer
22. The particles may be positioned atop the adhesive layer 22 or
at least partially embedded within the adhesive layer 22. The
particles are covered with an overlayer, such as conductive
material 18 that may act as a counterelectrode. The
counterelectrode may be, for example, indium tin oxide (ITO) that
is positioned on or under transparent layer 16. Together, the
layers form a re-addressable display material in which the
particles rotate in response to an electric or magnetic field that
is applied to the image formation layer via the conductive
substrate. The counterelectrode may be used to vary the field.
[0026] The capsules 10 may be or may contain any bichromal or
multichromal display materials such as bichromal beads,
electrophoretic particles, twisting cylinders and the like. The
size of the capsules is preferably substantially uniform. When
bichromal, the capsules and/or beads within the capsules are one
color (such as white) on one surface and a different color (such as
black) on the other surface. Multichromal capsules may have
different configurations. For signage applications, the diameter of
the capsules may be approximately 120 microns (.mu.m), within which
bichromal beads having a diameter of approximately 100 .mu.m may be
contained. Other capsule and particle sizes are possible within the
invention.
[0027] The capsules 10 form a closely-packed monolayer
configuration on the patterned adhesive layer 22. The
closely-packed monolayer configuration minimizes absorption of the
scattered light by the black or darker hemispheres, resulting in
substantial improvement in brightness.
[0028] By providing a patterned adhesive layer 22, the capsules 10
may be anchored according to a pre-determined geometry that
improves or maximizes packing density of the monolayer of capsules.
For example, as illustrated in FIG. 4, the adhesive layer 22 may be
patterned to provide raised elements at positions that are
separated from each other at distances that are just slightly more
than the diameter of the capsules. Thus, as illustrated in FIG. 3,
when the adhesive layer 22 receives the capsules 10, the capsules
are positioned in a closely packed monolayer.
[0029] FIG. 5 illustrates an exemplary pattern in accordance with
one embodiment. Referring to FIG. 5, the raised elements of the
adhesive layer 22 are shown to be patterned in a hexagonal manner
atop the substrate 14. The pattern may repeat over a larger area of
the substrate as shown, and other patterns are possible. The
hexagonal pattern such as that shown may provide a closely packed
monolayer with up to 90% or more of surface coverage. For example,
as shown in FIG. 6, when capsules 10 are positioned atop the
patterned layer, the capsules may be densely packed. Such a close
packing arrangement may result in a display material that exhibits
a high white reflectance and contrast, a smaller thickness (which
allows for a lower switching voltage), and improved resolution.
[0030] The adhesive layer may fix the capsules in place so that the
capsules form a desired pattern when the capsules come into contact
with the adhesive. For example, FIG. 5 shows a hexagonal adhesive
layer. Other geometries can be used, such as a substantially
hexagonal array, an at least substantially rectangular array, an at
least substantially rhomboidal array and other shapes. When the
capsules are fixed in place, the beads or particles inside of the
capsules may rotate or otherwise move in response to an applied
field.
[0031] The size and spacing of the adhesive later may vary in
accordance with the desired application. As illustrated in FIGS. 4
and 5, the adhesive layer 22 may include dots, ridges or raised
elements of adhesive material. The size and center-to-center
spacing of the raised elements will depend on the size of the
capsules used and the desired geometry in order to optimize capsule
packing density. For example, in display sign applications, the
capsules may have a diameter of about 120 microns (.mu.m), and the
capsules may be substantially uniform in size in order to optimize
performance. In such an application, the adhesive layer may have a
height or thickness of about 0.1 to about 20 .mu.m. The width of
the raised elements in this example may be about 5% to about 20% or
even to about 50% of the diameter of the capsule. The
center-to-center distance of the raised elements is preferably
slightly more than 120 .mu.m to provide close packing density. Of
course, other sizes, heights and distances are possible, and they
may be necessary with different size capsules. For example, smaller
capsules may be used in applications requiring higher resolution,
and the sizes associated with the patterned adhesive layer will
also be smaller in such applications.
[0032] The adhesive layer 22 may be made of any suitable adhesive
material, including but not limited to pressure-sensitive
adhesives, heat-activated adhesives (i.e., those with adhesive
properties that change with temperature) and/or light-activated
adhesives (i.e., those with adhesive properties that change with
light exposure). Exemplary materials include thermoplastic and
thermosetting adhesives such as copolymers of styrene and acrylate,
polyester resins, polyurethane, copolymers of acrylonitrile and
vinylidene chloride, polyvinyl acetate, polyvinyl butyral,
polyolefins, cyanacrylates, silicone and/or epoxy. Other suitable
materials may also be used.
[0033] In an embodiment, a display member may be created by
depositing a patterned adhesive layer onto a substrate using any
suitable coating technique, including coating techniques known in
the art such as screen printing, ink jet printing, spray coating,
gravure roll coating, and the like. For light activated adhesives,
a photo patterning or other suitable technique may be used.
[0034] The capsules may be applied to the adhesive layer using any
suitable means, such as by cascading them over the patterned
adhesive layer. Only the capsules that directly contact the
patterned adhesive will be retained, yielding an at least
substantially uniform, closely-packed, monolayer of coating.
Coating uniformity may be further improved by repeating the capsule
cascading process two or more times, and also by vibrating the
substrate during or after the cascading. Capsules that do not
attach to the adhesive may be removed by any number of methods,
including the use of gravity, suction and other methods.
[0035] Referring to FIG. 7, in an embodiment the capsules 10 may be
dispersed in an optional transparent matrix medium 30 that includes
transparent binder materials that protect the capsules. Suitable
binder materials include, and are not limited to, styrene-acrylic
copolymers such as styrene butylmethacrylate, styrene
ethylacrylate, acrylic acid copolymer, styrene-olefin copolymer,
polyurethane, polycarbonate, polyvinylacetate, silicone elastomers
and other materials.
[0036] Suitable substrates 14 include paper, polymeric films, ITO
coated polymeric films, glass, and other materials. The substrate
may include or be positioned atop a printed circuit board to allow
for selective application of fields to the image formation
layer.
[0037] The example below is merely representative of the work that
contributes to the teaching of the described embodiments and is not
to be restricted by the examples that follow.
[0038] Example 1: A patterned adhesive layer was produced on an
ITO-coated polyester substrate by spraying a 3M adhesive material
through a metal screen (25-85 mesh) to produce the desired pattern.
Encapsulated bichromal beads having a diameter of about 120 .mu.m
were cascaded over the patterned adhesive layer several times to
yield a substantially uniform coating. Microscopic examination
showed that the capsules were closely packed in a monolayer having
a geometry corresponding to the metal screen. A top electrode of
ITO-coated polyester was placed on top of the beads to form a
sandwiched structure. When an electric field was applied to the
structure, the beads oriented in one direction or another depending
on the polarity of the field. Reversing the polarity caused the
beads to change their orientation.
[0039] While the present invention is satisfied by embodiments in
many different forms, there is shown in the drawings and described
herein in detail, the preferred embodiments of the invention, with
the understanding that the present disclosure is to be considered
as exemplary of the principles of the invention and is not intended
to limit the invention to the embodiments illustrated. Various
other embodiments will be apparent to and readily made by those
skilled in the art without departing from the scope and spirit of
the invention. The scope of the invention will be measured by the
appended claims and their equivalents.
* * * * *